The present invention relates to a method for feeding a separator sheet, which is for use as a separator in a lead-acid battery, to an envelope apparatus which works the separator sheet in the form of a bag. The present invention also relates to an apparatus for feeding such a separator sheet.
In a general lead-acid battery, electrodes obtained by impregnating lead-alloy grids with an active material, are inserted in a separator. The separator is formed of a plastic material, such as micro-porous polyethylene, and are shaped like a bag. The separator serves to separate the positive and negative electrodes from each other inside the cell. In addition, the separator prevents the positive and negative electrodes from short-circuiting to each other even if the active material sheds from the grids. A number of ribs are integrally formed on the inner wall of the separator. The ribs help improve the diffusion of the electrolyte solution and adjust the pressure exerted on the electrodes.
The electrodes are inserted in the separator as follows. First of all, a plastic sheet (a micro-porous polyethylene sheet), which is for use as a separator, is wound to form a roll, and fed into the envelope apparatus. The plastic sheet is cut such that the sheet portion located inside the envelope apparatus has a predetermined length. The sheet obtained thereby is curved in the shape of a "U", and electrodes are inserted in the "U"-shaped sheet. With the electrodes inserted, the right and left ends of the sheet are connected together by fusion or by mechanically applying pressure thereto. As a result, the sheet is worked as a separator which is in the form of a bag.
In recent years, a glass mat is often used with the separator for fixedly pressing the active material against a grid and for preventing the separator from oxidizing. The case where such a glass mat is used is shown in FIG. 3. As shown in this FIGURE, a plastic sheet 1 for use as a separator and a glass mat 2 are stacked one upon the other, thereby obtaining a laminated member 3. The laminated member 3 is made to pass through the region between a pair of driving rolls 4 and 5. By these rolls, the sheet 1 and glass mat 2 of the laminated member 3 are tightly pressed against each other. The rolls 4 and 5 are rotated such that the laminated member 3 is fed to an envelope apparatus 6.
The driving rolls 4 and 5, by which the laminated member 3 made up of the sheet 1 and the glass mat 2 is compressed and fed toward the envelope apparatus 6, have a smooth surface formed of metal or rubber. When the laminated member 3 guided by the driving rolls 4 and 5 has been fed into the envelope apparatus 6 by a predetermined length, it is cut by means of a cutter 7 in such a manner that the sheet portion inside the envelope apparatus 6 has that predetermined length. The sheet portion is curved in the shape of a "U", and electrodes are inserted in the "U"-shaped sheet portion. With the electrodes inserted, the right and left ends of the sheet portion are connected together by fusion or by mechanically applying pressure thereto. As a result, the sheet is worked as a separator which is in the form of a bag.
A separator provided with a glass mat is shown in FIGS. 4 and 5. As shown in these FIGURES, the glass mat 2 is received in the separator S worked in the form of a bag. The glass mat 2 is bent inside the separator S, and an electrode 9 is inserted between the facing portions of the bent glass mat 2.
The separator sheet 1 and the glass mat 2 are cut in the stacked state, so that they are the same in length. The laminated member 3 made up of the sheet 1 and the glass mat 2 is bent, with the glass mat 2 located radially inside. At that time, the glass mat 2 inevitably shifts in position with reference to the sheet 1 (i.e., the separator S) located radially outside. As a result, the end portions of the glass mat 2 are projected upward from the separator S, as indicated by the broken lines in FIG. 5.
If the glass mat 2 is partially projected upward from inside the separator S, it is likely that particles of an active material will be deposited over the projected part of the glass mat 2, resulting in short-circuiting. To prevent this undesirable phenomenon, it may be thought to bond the sheet 1 and glass mat 2 together by use of a hot melt type adhesive before they are fed to the envelope apparatus 6.
However, this thought does not provide a satisfactory solution to the problem. In the case where the sheet 1 and the glass mat 2 are merely coated with an adhesive, a certain time is required before the adhesive hardens. In order to wait for the adhesive to satisfactorily harden, it is necessary to lower the rate at which the laminated member 3 is fed into the envelope apparatus 6. Alternatively, it is necessary to provide a long sheet feeding section between the driving rolls and the envelope apparatus. Hence, the productivity is lowered or the facility is inevitably large in size.